Still no clear answer to what killed 2 Mackey dogs during 2015 Iditarod

There are still no clear answers as to what caused the death of two dogs on four-time Iditarod champion Lance Mackey's team during the 2015 race.

In a news release Monday afternoon, Iditarod Trail Committee Chief Veterinarian Stu Nelson wrote that following evaluation of tissues collected from Mackey's dogs Wyatt and Stiffy, veterinarians found nothing that could definitively identify what caused the deaths. The two deaths were the first dog deaths on the trail since 2009. In 2013, a dropped dog from musher Paige Drobny's team that was left in the care of race officials died after it was left unprotected from blowing snow in frigid subzero temperatures in Unalakleet.

Nelson wrote that the "most probable" cause of death for Mackey's dogs was an acute cardiac event -- specifically "cardiac electrical disturbances" that likely precipitated the cardiac arrests since no abnormalities were identified in the tissues.

He wrote that a second review of pre-race electrocardiograms from the dogs did not reveal any existing abnormalities that would have put them at risk.

According to the release, there was no evidence of abuse or neglect. It also notes that the evaluation included a peer review by a second veterinary pathologist.

Efforts are still being made to pinpoint underlying factors that may have contributed to the dogs' deaths.

Both dogs died en route to checkpoints during the 2015 race, in which Mackey finished 43rd. According to race officials, necropsy results on Wyatt showed no abnormalities that could explain the death. Abnormalities were discovered during the necropsy of Stiffy, though Iditarod declined to say what those abnormalities were and concluded the cause of death was still unknown.